Is it possible to set the domain of the sessionid cookie asp sent

[iotaivy]

wo have several sites on a same server and these sites use subdomains of a
top domain,such as www.mycom.com, admin.mycom.com, forum.mycom.com.now we
want these sites to share the session state(such as loginning state),so
,without concerning a web farm or sharing session state among different top
domain, the simplest way to achive this must be to set the domain of the
sessionid cookies asp sent to our top domain.( if it is possible through the
iis metabase , registry or something else . )

If it isn't possible to set the domain of the sessionId coookie asp sent
,then,concerning a web farm or sharing session state among domains, Could you
guys recommand some third-pathy session management asp components or
servers(such as aSMS,but i can't download it anywhere)?

thanks